1. Field of the Invention
This invention relates to photoactive complexes of lanthanide metals with phosphine oxide, phosphine oxide-sulfides, pyridine N-oxide, or phosphine oxide-pyridine N-oxide ligands. It also relates to electronic devices in which the active layer includes a photoactive lanthanide complex.
2. Description of the Related Art
Photoactive compounds are of interest in a variety of applications, including analytical, bio-analytical and electronic uses. Extensive studies have been made of compounds of the lanthanide metals because of their characteristic sharp emission spectra with very narrow peak-widths. Analytical uses of luminescent complexes of lanthanide metals have been disclosed by, for example, Bell et al. in EP 556 005 and EP 744 451.
Organic electronic devices such as devices that emit light, such as light-emitting diodes that make up displays, are present in many different kinds of electronic equipment. In all such devices, a photoactive layer is sandwiched between two electrical contact layers. At least one of the electrical contact layers is light-transmitting so that light can pass through the electrical contact layer. The photoactive layer emits light through the light-transmitting electrical contact layer upon application of electricity across the electrical contact layers.
It is well known to use organic electroluminescent compounds as the active component in light-emitting diodes. Electronic devices using luminescent organometallic complexes of lanthanide metals have also been disclosed. In most devices the lanthanide centers are bound to diimine ligands, such as Skotheim et al., U.S. Pat. No. 5,128,587, and Borner et al., U.S. Pat. No. 5,756,224. Heeger et al. have reported devices using europium complexes blended with semiconducting conjugated polymers (Adv. Mater. 1999, 11, 1349). Devices containing lanthanide centers bound to phosphineoxide ligands have been disclosed in, for example, Kathirgamanathan et al. WO98/58037, Wenlian et al. Journal of the SID 1998, 6, 133, and Gao et al. Appl. Phys. Lett. 1998, 72, 2217.
There is a continuing need for improved photoactive lanthanide compounds. Furthermore, the synthesis and luminescent properties of lanthanide complexes bound to phosphine oxide, phosphine oxide-sulfide, N-oxide or phosphine oxide-pyridine N-oxide ligands have remained largely unexplored.